High-purity fused silica glass is typically made by a flame hydrolysis process, which may be a soot-to-glass process or a direct-to-glass process. In both the soot-to-glass and direct-to-glass processes, silica precursor is passed into the flame of a burner to generate soot. In the direct-to-glass process, the soot is collected on a substrate or mandrel, commonly referred to in the art as a “bait,” that is maintained at a temperature or range of temperatures conducive to immediate consolidation of the soot into dense glass. In the soot-to-glass process, the soot is collected on a bait that is maintained at a temperature or range of temperatures below which the soot can consolidate into dense glass. The soot accumulates on the bait to form a porous preform, which is subsequently consolidated into the dense glass in a separate step from the soot deposition step. To increase throughput or to make large parts, multiple burners are often used to generate multiple flames for converting the silica precursor into soot. The multiple burners are typically connected to a common manifold and receive a mixture of silica precursor and process gases supplied to the manifold to generate the soot. Each burner deposits soot over a small section of the bait. The amount and density of soot deposited on each small section of the bait may vary from one burner to the next due to factors such as differences in the burner design or dimensions and differences in the rate at which the mixture of precursor and process gases in the manifold is delivered to the burners. Consequently, there may be variations in composition, e.g., β-OH concentration, and/or physical properties, e.g., refractive index, within the final product. It is desirable to reduce or eliminate such variations in the final product.